rydberg unit vs rydberg constant

rydberg unit and rydberg constant both are nouns.

Word	Noun	Adjective	Verb	Adverb
rydberg unit	Yes	No	No	No
rydberg constant	Yes	No	No	No

As nouns, rydberg unit and rydberg constant are synonyms defined as:

rydberg unit and rydberg constant: a wave number characteristic of the wave spectrum of each element

Other synonyms of rydberg unit include rydberg.

rydberg unit (noun)	rydberg constant (noun)
a wave number characteristic of the wave spectrum of each element	a wave number characteristic of the wave spectrum of each element